Fix MinGW CI failures

[falbrechtskirchinger]

Attempt to workaround recent, frequent failures of the MinGW jobs by installing an internalized Chocolatey package hosted on GitHub.

NuGet package hosted here: https://github.com/falbrechtskirchinger/json/packages/1564692

---

I've since figured out how to create and upload a package without using Chocolatey and NuGet.

1. Download the Chocolatey NuGet package from here:
   https://community.chocolatey.org/packages/mingw/8.1.0
   (Gray download button at the bottom of the left sidebar.)
2. Unzip mingw.8.1.0.nupkg.
3. Open tools/chocolateyinstall.ps1 in an editor.
4. Download the 2 URLs listed near the top and save the files to the tools/ folder.
5. Replace the URLs with the local file names:

$toolsDir = "$(Split-Path -parent $MyInvocation.MyCommand.Definition)"

$packageName = 'mingw'
$url = "$toolsDir\i686-8.1.0-release-posix-dwarf-rt_v6-rev0.7z"
$checksum = 'adb84b70094c0225dd30187ff995e311d19424b1eb8f60934c60e4903297f946'
$url64 = "$toolsDir\x86_64-8.1.0-release-posix-seh-rt_v6-rev0.7z"
$checksum64 = '853970527b5de4a55ec8ca4d3fd732c00ae1c69974cc930c82604396d43e79f8'

(Don't forget the line defining $toolsDir.)
6) Zip the directory and rename it to *.nupkg. (Note that not all programs produce a ZIP file that Microsoft's implementation can read. I successfully used my command line zip tool from http://www.info-zip.org/.)
7) Upload to nuget.org.
8) The package can now be downloaded from here: https://www.nuget.org/api/v2/package/mingw/8.1.0

Optionally, it might be a good idea to change the package ID.

1. Open mingw.nuspec.
2. Change the <id> element value as desired, e.g. nlohmann-json.mingw.
3. I don't know if the *.nuspec file name has to match. Maybe rename it to the ID, to be safe.

[coveralls]

Coverage remained the same at 100.0% when pulling c282499 on falbrechtskirchinger:ci-mingw3 into 2d48a4d on nlohmann:develop.

[nlohmann]

Looks good to me.

[nlohmann]

• Is the header really needed to download the package?
• I don't know what you mean with

I've since figured out how to create and upload a package without using Chocolatey and NuGet.

[falbrechtskirchinger]

• Is the header really needed to download the package?

Yes. It requires either a GITHUB_TOKEN or a PAT.
https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-nuget-registry#authenticating-with-github_token-in-github-actions

Also, you can try to download the file in your browser. You'll be greeted by a login prompt.
https://nuget.pkg.github.com/falbrechtskirchinger/download/mingw/8.1.0/mingw.8.1.0.nupkg

• I don't know what you mean with

I've since figured out how to create and upload a package without using Chocolatey and NuGet.

I started with the Chocolatey guide for internalizing packages which uses both Chocolatey (choco.exe) and NuGet (nuget.exe). The former runs using WINE, and the latter is natively available on Linux (as part of .NET).
choco is used to create the package and NuGet is required to publish it to the GitHub registry.

In case you want to be able to recreate these steps, you'd be in for quite a bit of work. Luckily, the package can in fact be created without these tools, and by using the official nuget.org registry, you could upload the package without a tool on the website.

This is only relevant if you want to create and host these packages yourself.

[nlohmann]

Thanks for clarifying. I currently don't plan to host them myself.